This invention is related to the field of digital signal processing, and more particularly to a television signal receiver system including a filter for rejecting co-channel interference.
Recent developments in the field of video signal processing have produced digital high definition television (HDTV) signal processing and transmission systems. An HDTV terrestrial broadcast system recently proposed as the Grand Alliance system in the United States employs a digital transmission format for transmitting a packetized datastream. The Grand Alliance HDTV system is a proposed transmission standard that is under consideration in the United States by the Federal Communications Commission through its Advisory Committee on Advance Television Services (ACATS). A description of the Grand Alliance HDTV system as submitted to the ACATS Technical Subgroup on Feb. 22, 1994 (draft document) is found in the 1994 Proceedings of the National Association of Broadcasters, 48th Annual Broadcast Engineering Conference Proceedings, Mar. 20-24, 1994.
The proposed Grand Alliance HDTV system is a simulcast system. In such a system, two versions of the same program material may be broadcast simultaneously via separate standard 6 MHz channels. One of the two program versions contains standard definition NTSC information broadcast on one channel, while the other contains high definition information broadcast on the other 6 MHz channel. In practice, a simulcast system may utilize two adjacent 6 MHz NTSC channels, eg., VHF channels 3 and 4, to convey the standard and high definition information, respectively. The high definition version of a simulcast system can be implemented in a standard 6 MHz channel by using data compression techniques. The standard NTSC information and the HDTV information are received independently by respective standard NTSC and HDTV receivers. When standard NTSC receivers are eventually replaced by HDTV or dual-standard receivers, the channels used by standard NTSC signals will become available for other purposes. Thus the simulcast concept prevents the vast number of pre-existing standard NTSC receivers from becoming obsolete as soon as HDTV broadcasting is introduced, and permits expanded broadcasting services in the future when the channels occupied by standard NTSC signals become available.
The rejection of co-channel interference is a factor in a simulcast system since co-channel interference may severely degrade or disrupt the operation of a high definition television receiver. Co-channel interference may result when two different television signals are transmitted on the same broadcast channel and are received simultaneously. The interfering signal components typically are the picture carrier (located 1.25 MHz from the lower band edge), the chrominance subcarrier (located 3.58 MHz higher than the picture carrier) and the sound carrier (located 4.5 MHz higher than the picture carrier). The likelihood of co-channel interference occurring is a function of various factors, such as the broadcast distance between the two channels and the transmission power of the channels, for example.